diff --git a/plone/dexterity/fti.py b/plone/dexterity/fti.py
index f5c2e4b..131077b 100644
--- a/plone/dexterity/fti.py
+++ b/plone/dexterity/fti.py
@@ -367,11 +367,11 @@ def unregister(fti, old_name=None):
     site_manager = getSiteManager(site)
     
     portal_type = old_name or fti.getId()
+
+    notify(SchemaInvalidatedEvent(portal_type))
     
     site_manager.unregisterUtility(provided=IDexterityFTI, name=portal_type)
-    unregister_factory(fti.factory, site_manager)
-    
-    notify(SchemaInvalidatedEvent(portal_type))
+    unregister_factory(fti.factory, site_manager)    
 
 def unregister_factory(factory_name, site_manager):
     """Helper method to unregister factories when unused by any dexterity
@@ -465,4 +465,4 @@ def ftiModified(object, event):
             model = fti.lookupModel()
             syncSchema(model.schema, schema, overwrite=True)
         
-        notify(SchemaInvalidatedEvent(portal_type))
\ No newline at end of file
+        notify(SchemaInvalidatedEvent(portal_type))
diff --git a/plone/dexterity/schema.py b/plone/dexterity/schema.py
index 38ea083..5188299 100644
--- a/plone/dexterity/schema.py
+++ b/plone/dexterity/schema.py
@@ -115,7 +115,8 @@ class SchemaCache(object):
     @synchronized(lock)
     def invalidate(self, portal_type):
         fti = queryUtility(IDexterityFTI, name=portal_type)
-        invalidate_cache(fti)
+        if fti is not None:
+            invalidate_cache(fti)
 
 
 SCHEMA_CACHE = SchemaCache()